Detection of deteriorated electrical connections in a meter using temperature sensing and time-variable thresholds

ABSTRACT

A utility meter includes a meter housing that supports at least one current coil, a temperature sensor, and a processing circuit coupled to both. The current coil can be coupled to receive heat energy from a meter socket. The temperature sensor disposed generates a sensor signal based on a temperature within the meter housing. The processing circuit obtains the sensor signal and generates meter temperature information based at least in part thereon. The processing circuit also obtains a first predetermined threshold based on at least one of time of day information and date information. The processing circuit also determines whether an abnormal condition exists by comparing the meter temperature information to a value based on the first predetermined threshold, and generates an output signal to a memory, display or communication circuit responsive to determining that the abnormal condition exists.

Cross-reference is made to co-pending application, U.S. Ser. No.15,719,086, which was filed on Sep. 28, 2017.

FIELD OF THE INVENTION

This invention relates generally to electricity meters, and moreparticularly, to electricity meters having temperature sensing.

BACKGROUND

Utility meters are devices that, among other things, measure theconsumption of a utility-generated commodity, such as electrical energy,gas, or water, by a residence, factory, commercial establishment orother such facility. Utility service providers employ utility meters totrack customer usage of the utility-generated commodities. Utilityservice providers track customer usage for many purposes, includingbilling and demand forecasting.

Electricity meters that measure energy consumption or power consumptiontypically connect between a utility power line and a load. For example,an electricity meter for a residential customer is often connected atthe point at which the electrical system of the residence connects tothe utility line. The meter may thereby perform measurements regardingthe energy consumed by the load.

Electricity meters often include one or more electrical contacts acrosswhich the load voltage and a significant amount of current may be found.For example, meters often have blades that connect to the power line toenable the measurement of load current and load voltage from within themeter. The blades are received by the jaws of a meter mounting device ofthe building. Spring compression within the jaws retains the bladessecurely. If the meter is to be replaced or repaired, then the meter maybe pulled out of the mounting device, and hence the blades out of thejaws. Although the blades and jaws are usually mechanically robust, theyare nevertheless subject to wear, and possibly corrosion, particularlyif the meter has been removed or replaced several times. If wear on thejaws is significant, or if the jaws have corrosion, then there is apossibility of introducing a non-trivial resistance at the jaw/bladeconnection, which is undesirable. In some cases, the jaw/bladeconnection can undesirably deteriorate to a condition in which arcingoccurs.

Likewise, certain meters have switches that allow for disconnection ofelectrical service to a load. For example, many meters allow for remotedisconnection of the load. Such switches necessarily must havesubstantial contacts because they carry the entire current of the loadwhen the switch is closed. If these switches are used with somefrequency, then there is a potential for degradation. Degradation of theswitch contacts increases the resistance over the switch contacts. Aswith the meter blades and jaws, resistance creates additional power losswithin the meter, and potentially arcing, both undesirable.

It is known to detect the possible deterioration of meter switchcontacts by measuring the resistance and/or current through the contactswithin the meter. If the resistance exceeds a threshold, then anindication of potential need for maintenance is displayed ortransmitted. Such a method is taught, for example, in U.S. Pat. No.7,683,642, issued Mar. 23, 2010. One limitation of this technique isthat it can require extra elements to carry out the resistancemeasurement, thereby adding material cost and manufacturing complexity.

It is also known to monitor the temperature of the sockets and jaws ofthe meter for overheating. The detection of an overheat condition in thesockets and jaws of the meter can indicate an arcing condition, or othercondition, such as increased resistance, requiring maintenance. Such amethod is discussed, for example, in U.S. Pat. No. 7,513,683. Thismethod, however, requires that the temperature sensing device beattached to a mass in thermal contact with the electrical connection.This technique, though simple, cannot be applied in meter designs wherethe temperature sensing device is isolated from the electricalconnection by some sort of significant insulator, such as an air gap. Insuch meter designs, the measured temperature can be distorted to asignificant extent by ambient temperature and other normal operationswithin the meter. As a consequence, the threshold must be high enough toavoid false positives due to other conditions causing a temperature risein and around the meter blades.

Another known method of detecting the presence of arcing or other meterblade/socket malfunction includes monitoring RF noise within the meter.In particular, arcing between the meter blades and the meter socketcauses emission of certain RF noise that may be monitored. Such a methodis described in U.S. Patent Publication No. 2014/0327449. Such asolution, however, cannot readily distinguish arcing from other sourcesof RF noise. Thus, sometimes such a method includes monitoring othermeter phenomena, such as internal temperature, so that multiplephenomena can confirm the condition. However, such a solution requiresan RF receiver and has the complexity associated with monitoringmultiple factors to determine if arcing is present.

Thus, a continuing need exists to detect possible issues due todeterioration of high-power switch contacts in a meter or a meter socketthat can reliably and efficiently determine the presence of amaintenance issue.

SUMMARY

Different embodiments described herein address the above-cited need, aswell as others, by using a compensated temperature measurement todetermine if an overheat condition exists. Moreover, other embodimentsdetermine whether a measured temperature (with or without compensation)is outside of normal ranges based on the time of year and the time ofday.

A first embodiment is a utility meter that includes a meter housing thatsupports at least one current coil, a temperature sensor, and aprocessing circuit coupled to both. The current coil can be coupled toreceive heat energy from a meter socket. The temperature sensor disposedgenerates a sensor signal based on a temperature within the meterhousing. The processing circuit obtains the sensor signal and generatesmeter temperature information based at least in part thereon. Theprocessing circuit also obtains a first predetermined threshold based onat least one of time of day information and date information. Theprocessing circuit also determines whether an abnormal condition existsby comparing the meter temperature information to a value based on thefirst predetermined threshold, and generates an output signal to amemory, display or communication circuit responsive to determining thatthe abnormal condition exists.

The above-described features and advantages, as well as others, willbecome more readily apparent to those of ordinary skill in the art byreference to the following detailed description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic block diagram of a metering system for afacility that includes a mounting device and a utility meter;

FIG. 2 shows an exemplary set of operations carried performed by theprocessing circuit of the meter of FIG. 1 to generate meteringinformation;

FIG. 3 shows a flow diagram of an exemplary meter heat monitoringroutine that may be performed by the processing circuit of the meter ofFIG. 1;

FIG. 4 shows in further detail an exemplary set of operations that maybe performed as part of the meter heat monitoring routine of FIG. 3;

FIG. 5 shows in further detail an exemplary set of operations that maybe performed as another part of the meter heat monitoring routine ofFIG. 3;

FIG. 6 shows an exemplary timeline of the values of a sample operationof the routine of FIG. 3;

FIG. 7 shows an exemplary timeline of the values of a sample operationof an alternative embodiment of the routine of FIG. 3; and

FIG. 8 shows in further detail an exemplary set of operations that maybe performed as part of the alternative embodiment of the meter heatmonitoring routine of FIG. 3;

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the disclosure is therebyintended. It is further understood that this disclosure includes anyalterations and modifications to the illustrated embodiments andincludes further applications of the principles of the disclosure aswould normally occur to one skilled in the art to which this disclosurepertains.

As shown in FIG. 1, a metering system 100 for a facility 104 includes amounting device 108 and a utility meter 112 associated with electricalpower distribution lines 116 that distribute electrical energy from autility 120. In the exemplary arrangement of FIG. 1, the mounting device108 includes two line-side sockets 124 electrically connected to thedistribution lines 116, and two load-side sockets 128 electricallyconnected to the facility 104. The sockets 124, 128 are formed frommetal and are configured to withstand high currents and voltages. Inother embodiments, the mounting device 108 includes any suitable numberof sockets 124, 128 formed from any suitable material.

The utility meter 112 includes a housing 136, at least one primary coilor current coil 140 (two shown in FIG. 1), at least one secondary coil144 (two shown in FIG. 1), at least one voltage sensor 141 (two shown inFIG. 1), a temperature sensor 160, and a metrology circuit 152. In thisembodiment, the utility meter 112 also includes memory 180, atransceiver 184, and a display 188. The housing 136 is an electricitymeter housing, as is known in the art, which supports and protects metercomponents from tampering and harmful environmental conditions. In thisembodiment, the voltage sensors 141, the secondary coils 144 and memory180, the transceiver 184, the display 188 and the metrology circuit 152are all contained within an interior of the housing 136. Preferably, aprinted circuit board 137 supports the memory 180, the transceiver 184,the display 188 and the metrology circuit 152. The printed circuit board137 is spaced apart from the high current components, i.e., the currentcoils 140, by at least two inches.

The current coils 140, also referred herein to as primary coils 140, areelectrical conductors (e.g. copper conductors) that are located at leastpartially within and supported by the housing 136. The current coils 140each include two blades 156, which are configured to partially extendfrom the housing 136. The blades 156 are configured to provide amechanically and electrically sound connection between the current coils140 and the sockets 124, 128. Specifically, the blades 156 areconfigured to be received by the sockets 124, 128 to operably connectthe current coils 140 to the sockets such that electrical current may betransferred through the utility meter 112. In other words, theelectrical current drawn by the facility 104 passes through the currentcoils 140 when the blades 156 are received by the sockets 124, 128. Inaddition, the current coils 140 and the blades 156 may also mechanicallysupport the meter 112 in a mounted position (as shown in FIG. 1) on themounting device 108. Also, heat energy generated within or on thesockets 124, 128 is transferred to the current coils 140 through theblades 156, since the current coils 140 and the blades 156 are typicallyformed from metal and are positioned in contact with the sockets 124,128.

The secondary coils 144, which may suitably be part of a so-calledcurrent transformer, are disposed in a current sensing relationship withrespect to the current (primary) coils 140. As is known in the art, acurrent transformer includes at least one secondary coil (e.g. thesecondary coils 144) wrapped about a toroidal core, not shown. At leastone of the primary coils 140 passes through the center of the toroidalcore. Accordingly, the primary coils 140 and the secondary coils 144 areconfigured as an electrical transformer. Regardless of the specificembodiment, the secondary coils 144 are configured to generate a scaleddown version of the current passing through the primary coils 140. Eachof the secondary coils 144 is operably coupled, e.g. through acorresponding burden resistor 145, to provide a current measurementsignal representative of the current passing through the primary (orcurrent) coils 140 to the metrology circuit 152.

The voltage sensors 141, each of which may suitably comprise a resistivedivider, are disposed in a voltage sensing relationship with respect tothe current coils 140. The voltage sensors 141 are configured togenerate a scaled down version of the line voltage on the current coils140, which is representative of the voltage delivered to the load. Thevoltage sensors 141 are operably coupled, to provide a voltagemeasurement signal representative of the voltage on the current coils140 to the metrology circuit 152.

The metrology circuit 152 is any suitable circuit(s) configured togenerate metering data or consumption data by detecting, measuring, anddetermining one or more electricity and/or electrical energy consumptionvalues based on electrical energy flowing from the line-side sockets 124to the load-side sockets 128. Specifically, the metrology circuit 152uses at least the voltage measurement signal and the current measurementsignal to determine the metering data. The utility 120 typicallyaccesses the metering data for billing purposes as well as otherpurposes.

In this embodiment, the metrology circuit 152 includes ananalog-to-digital converter (“ADC”) 162, a processing circuit 164, allpackaged within a single integrated circuit (“chip”) package 170. Theintegrated circuit package 170 may also include all or part of thememory 180. In general, the ADC 162 is operably coupled to receive thevoltage measurement signals from the voltage sensors 141, and togenerate digital voltage measurement signals therefrom. The ADC 162 islikewise operably coupled to receive the current measurements signalsfrom the secondary coils 144 and generate digital current measurementsignals therefrom.

The processing circuit 164 includes one or more processing devices andaccompanying support circuitry, configured to carry out programoperations and processing. The processing circuit 164 is operablycoupled to receive the digital voltage and current measurement signalsfrom the ADC 162, and is programmed and/or otherwise configured togenerate metering information therefrom. For example, the processingcircuit 164 may suitably use known computational methods to determineenergy consumption (e.g. kw-hrs, VARS, etc.) using the digital voltageand current measurement signals. The processing circuit 164 alsoexecutes software instructions to perform control operations, and otheroperations described herebelow. The processing circuit 164 is operablyconnected to receive the software instructions from the memory 180.

With reference still to FIG. 1, the temperature sensor 160 is a sensordevice and accompanying circuit that are configured to generate a sensorsignal based on a temperature within the meter housing 136. Thetemperature sensor 160 is configured to provide the sensor signal to theprocessing circuit 164. To reduce manufacturing costs, the temperaturesensor 160 can be disposed on or supported by the printed circuit board137. Specifically, in this embodiment, the temperature sensor 160 isincluded in the integrated circuit package 170 in which the processingcircuit 164 is disposed. Examples of commercially available meterprocessing packages that include a suitable processing circuit andtemperature sensor include the model 71M6513, 71M6521, and 71M6533metering ICs available from Silergy Corp.

In particular, since the current coils 140 and the sockets 124, 128 areconfigured to conduct heat energy, the current coils 140 have atemperature that is in part based on the temperature of the sockets 124,128. The current coils 140 are largely disposed within the interior ofthe meter housing 136, and thus heat conveyed from the sockets 124, 128cause the temperature within the meter housing 136 to rise.Consequently, the temperature sensor 160 is configured to indirectlysense the temperature within or on the sockets 124, 128 by sensing thetemperature within the meter housing 136.

Because the temperature sensor 160 in this embodiment is located on thecircuit board 137 away from current coils 140 and blades 156, themeasurement of the temperature sensor 160 less directly reflects heatgenerated within the connection between the meter jaws 124, 128 and themeter blades 156. To this end, normal operational heat of the metrologycircuit 152, as well as environmental heat (weather), and other factorscan affect the temperatures within the meter housing 136. Accordingly,the processing circuit 164 in this embodiment is configured to determinea temperature adjustment value that is intended to approximate theambient heat or meter self-heating, or in other words, heat that ispresent due to factors other than a malfunctioning connection betweenone or more of the sockets 124, 128 and blades 156.

In general, the temperature adjustment value is calculated based on thecurrent passing through current coils 140, and includes a constant valuethat approximates the self-heating of the metrology circuit 152. As willbe discussed below in detail, the processing circuit 164 is furtherconfigured to process the temperature adjustment value using an infiniteimpulse response filter (or other low pass filter), to account for thefact that changes in current do not immediately result in temperaturechange. As will also be discussed below in detail, the processingcircuit 164 is further configured to determine if the difference betweenthe temperature sensor value and the temperature adjustment value, whichapproximates heating due to abnormal conditions, exceeds a threshold,thus indicating a heat-generating malfunction.

With continued reference to FIG. 1, the utility meter 112 in thisembodiment further includes an optional disconnect unit 172. Thedisconnect unit 172 is operably coupled to the current coils 140 and themetrology circuit 152 and is configurable in a closed state (firststate) and an open state (second state). In the closed state, a closedcircuit is formed in the current coils 140, which enables electricalpower transfer from the utility 120 to the facility 104 (i.e. the load)through the distribution lines 116. In the open state, an open circuitis formed in the current coils 140, which prevents electrical powertransfer from the utility 120 to the facility 104 through thedistribution lines 116. Specifically, in the open state electricalcurrent is prevented from flowing from the line-side sockets 124 to theload-side sockets 128. The disconnect unit 172 includes a relay or anyother suitable device that controllably disconnects and re-connectselectrical power to the facility 104. Because the disconnect unit 172contains switch contacts, not shown, that carry the full load current tothe facility 104, such contacts can also degrade to a point at whichthey create excess heat within the meter housing 136. Any overheatconditions caused by degradation of the disconnect unit 172 will also bedetected by the sensor 160 and processing circuit 164 performing theoperations described herein.

Moreover, as described below, the metrology circuit 152 may beconfigured to control the state of the disconnect unit 172 based on thedetection of overheat conditions within the meter housing 136.

The memory 180 is operably coupled to the processing circuit 164 and isconfigured to store metering data generated by the metrology circuit152. The memory 180 may include separate devices within or external tothe integrated circuit package 170. Additionally, the memory 180 isconfigured to store look-up tables and program data for operating thetemperature sensor 160 and the processing circuit 164 according to themethods described herein, as well as storing any other electronic dataused or generated by the metrology circuit 152. The memory 180 is anon-transitory machine readable storage medium. While the memory 180 isshown in the drawing as being external to the integrated circuit package170, the memory 180 shall be considered to encompass data and programstorage both internal to and external to the integrated circuit package170. In a preferred embodiment the data values discussed below inconnection with FIGS. 3 through 8 may be programmed externally, throughthe transceiver 184, to allow for the values to be location-specific, aswell as meter-configuration specific.

The transceiver 184 is operably coupled to the processing circuit 164and is configured to send electric data to the utility 120 and/or to anexternal unit (not shown), and to receive electric data from the utilityand/or the external unit. In one embodiment, the transceiver 184 is aradio frequency (“RF”) transceiver operable to send and to receive RFsignals. In another embodiment, the transceiver 184 includes anautomatic meter reading (AMR) communication module configured totransmit data to an AMR network and/or another suitable device. Thetransceiver 184 may also be configured for data transmission via theInternet over a wired or wireless connection. In other embodiments, thetransceiver 184 is configured to communicate with an external device orthe utility 120 by any of various means used in the art, such as localoptical communications, power line communications, telephone linecommunications, or other means of communication.

The display 188 is operably coupled to the processing circuit 164 and isconfigured to display data associated with the utility meter 112 in avisually comprehensible manner. For example, the display 188 may beconfigured to display consumption data, the state of the disconnect unit172, and the sensed temperature within the meter housing 136, forexample. The display 184 may be any suitable meter display device, suchas a liquid crystal display unit, for example.

In operation, the metering system 100 operates to measure and quantifyelectrical energy provided to the facility 104 from the utility 120 viathe power distribution lines. To this end, line voltages and linecurrents flowing from the distribution lines 116 to the facility 104pass through the sockets 124 and blades 124 to the current coils 140 a,140 b. The secondary coils 144 detect the line currents and generatescaled down versions of the line current on the current coils 140 a, 140b. The secondary coils 144 provide to the ADC 162, via correspondingburden resistors 145, a current measurement signal representative of thecurrent passing through each of the current coils 140 a, 140 b. Thevoltage sensors 141 obtain the line voltage from each of the currentcoils 140 a, 140 b, and generate a scaled down version of each linevoltage, which is representative of the voltage signals delivered to theload. The voltage sensors 141 are operably coupled to provide a voltagemeasurement signal representative of each of the line voltages to theADC 162.

The ADC 162 digitizes the voltage and current measurement signals togenerate streams of samples (digital waveforms) having valuesapproximating the voltage and current measurement signals. The ADC 162provides the digital voltage and current measurement signals to theprocessing circuit 164.

The processing circuit 164 uses the digital voltage and measurementsignals to generate the metering data. Such metering data can includesand accumulated energy consumption value (e.g. kw-hrs, VARS, etc.), RMSvoltage values, RMS current values, and instantaneous energy values,among other things. To this end, the processing circuit 164 in thisembodiment performs the operations of FIG. 2. It will be appreciatedthat many other types of operations and calculations may be performed inaddition to those in FIG. 2, and not all of the calculations of FIG. 2need be performed to carry out at least some embodiments of theinvention.

In step 205, the processing circuit 164 receives digital voltage andcurrent measurement values (e.g. samples) for the current time, t. Instep 210, the processing circuit 164 calculates at least one energyconsumption value, for example, accumulated value AEC(t) as a functionof the previous value, AEC(t−1), and the newly received digital voltageand current measurement values. Various sample-based energy and powercalculations are known to those of ordinary skill in the art. Forexample, it is not known to multiply contemporaneous voltage and currentsamples, and to accumulate the totals over time.

In step 215, the processing circuit 164 generates one or more currentmagnitude values representative of the magnitude of current flowingthrough the current coils 140. For example, the processing circuit 164can generate root-mean-square (“RMS”) current calculations for each ofthe current coils 140 a and 140 b. For example, the value IA maysuitably be the RMS current for the current detected on the current coil140 a at time t, and the value IB may suitably be the RMS current forthe current detected on the current coil 140 b at time t. The processingcircuit 164 generates such RMS values in any traditional manner based onthe samples of the digital current measurement signal from the priorseveral AC cycles of the line current. For example, in a 60 Hz system,the samples for the last one second cover sixty AC cycles, and thusprovide a reasonable RMS voltage calculation. Fewer or more samplesmaybe used. It will be appreciated that step 215 need not be performedevery time the energy consumption value AEC(t) is updated in step 210.It may be sufficient to update the current measurement values everysecond, every few seconds, or even every minute or longer.

In step 220, the processing circuit generates other energy-relatedvalues, which can include RMS voltage per line, and/or power factorrelated values. The calculation and use of such values would be known tothose of ordinary skill in the art.

In step 225, the processing circuit 164 stores the current magnitudevalues in the memory 180, and may also store in the memory 180 any ofthe values generated in steps 210 or 220. In particular, because meter112 includes two current sensors, the processing circuit 164 maysuitable calculate and store the two current magnitude values IA and IBin step 225. In steps 230, the processing circuit 164 causes the display188 to display one or more of the values calculated in steps 210, 215 or220. Typically, the processing circuit 164 will cause the display todisplay the energy consumption value AEC(t) generated in step 210. Itwill again be appreciated that steps 225 and 230 need not be executedevery time a new energy consumption value is calculated.

In addition to such ongoing functions, the processing circuit 164 cancontemporaneously perform other tasks. In this embodiment, theprocessing circuit 164 performs a heat monitoring routine thatdetermines whether there is a heat-related issue with the meter 112,such as from arcing between any of the sockets 124, 128 and any of themeter blades 156.

FIG. 3 shows a flow diagram of an exemplary meter heat monitoringroutine 300 that may be performed by the processing circuit 164. As isknown in the art, the processing circuit 164 may be contemporaneouslyperform other steps of other routines, such as those of FIG. 2, whileexecuting the steps of monitoring routine 300. The processing circuit164 is preferably configured to execute the routine 300 at regularintervals t, such that each iteration a predetermined time period fromthe previous iteration. An exemplary interval may be within the range oft=0.1 seconds to 1.0 second.

In step 305, the processing circuit 164 obtains at least one currentmagnitude value I_(SUM) that is representative of the sum of the currentmagnitudes through the current coils 140 a, 140 b. In the embodimentdescribed herein, the processing circuit 164 obtains the most recentlystored RMS current values IA and IB (see step 215, discussed above) fromthe memory 180. The processing circuit 164 then adds the two numberstogether to yield I_(SUM). In other words, the processing circuit 164performs the following calculation: I_(SUM)=IA+IB. Alternatively, othervalues representative of the total current magnitude delivered throughthe current coils 140 a, 140 b may be used. It will be appreciated thatin an embodiment in a three-phase meter having three current coils, theprocessing circuit 164 would obtain a value representative of the sum ofthe current magnitudes in all three current coils.

In step 310, calculation constants A, B, C, and α are retrieved from thememory 180. The calculation constants A, B, and C represent thecoefficients of the equation that models the self-heating temperaturecomponent of the meter 112. In accordance with the embodiments describedherein, the self-heating temperature value, CSH, is a measure of theinternal heating of the meter that occurs due to normal meteroperations. As will be discussed below, the value CSH is calculatedusing the generalized equation:CSH=A*I _(SUM) ² +B*I _(SUM) +C  (1)As will be discussed below, the self-heating temperature value CSH isused as an adjustment to the measured temperature to yield anapproximation of the heating within the meter 112 that is due toabnormal conditions, as opposed to normal internal self-heating. In thisembodiment, the value CSH is furthermore filtered to account for thetime lag between current swings and the corresponding temperature changein the current coils 140. The value a is a coefficient for that filter,which is in the form of an infinite impulse response filter.

As can be seen in equation (1), the self-heating within the meter 112includes a portion that is dependent on load current (I_(SUM)), and aportion that is independent of load current. To this end, normalself-heating occurs due to load current flowing through the currentcoils 140, and other factors, such as the operation of the processingcircuit 164 and/or communications circuits. The portion of self-heatingdue to load current has been found in one typical type of meter to be0.1° to 0.15° C./amp, with an exponential increase after the currentreaches 160 amps. These values will vary from meter to meter and may bedetermined empirically.

The value of A represents the exponential coefficient, and thereforewill be well below unity for temperatures below that which theself-heating becomes exponential with current. Thus, the example wherethe current increases exponentially after 160 amps, the value A shouldbe below 1/160 or 0.00625, assuming the value of CSH is in amps. Thevalue of B, however, represents the proportional portion of the loadcurrent based-self heating, and therefore will in the range 0.1 to 0.15,assuming the value of CSH is in amps.

The value of C is not related to load current, and represents anapproximation of all other normal self-heating within the meter 112.Such other self-heating will be present even when little or no currentis flowing through the current coils 140 a, 140 b. It has been foundthat the load current independent self-heating in one exemplary meter isin the range of 4° C. to 10° C.

The values of A, B, and C can be determined empirically for every meterconfiguration. In particular, temperature readings can be taken from thetemperature sensor 160 at various load current levels, in a facilitywith a known ambient (environmental temperature). The load current wouldpresumably be applied through the current coils 140 a and 140 b in acontrolled condition with properly conducting electrical contacts. Eachtemperature reading should be taken after a delay from the applicationof the load current in order to ensure that the steady-state temperatureis reached for each load current level. The differences between thetemperature readings and the known ambient temperature would then beplotted as a function of load current level. Traditional curve-fittingtechniques can be used to develop the best fit coefficients A, B, C forthe function CSH=A*I_(SUM) ²+B*I_(SUM)+C.

The value of α is the decay factor of the IIR filter. The filter manysuitably have the form of:CSH′=α*CSH+(1−α)*PREV_CSH′,  (2)where n is the index, discussed above, that is incremented each time theroutine 300 are executed. In general, α represents the decay factor forincreasing or decreasing heat radiated by the current coils 140 a, 140 bresponsive to a change in current. For example, a current coil thattransitions from carrying only one (1) amp to carrying one hundred sixty(160) amps will not have the same temperature immediately as it will ifit remains at one hundred sixty (160) amps for twenty minutes. The valueof α will vary based on the physical characteristics of the currentcoils 140 a, 140 b, and the time period between successive executions ofthe routine 300. The factor α may also be determined empirically byapplying transitions in load current and taking temperature measurementsat various intervals after the transition.

It will be appreciated that in lieu of retrieving the values A, B, C,and α separately from memory 180, the values may be embedded within theactual software executed by the processing circuit 164, for example,when carrying out the calculations of steps 315 and 320 below. It willbe appreciated that such program itself would be stored in the memory180, and thus that the values A, B, C, and α would thus be stored in thememory 180 either way. However, the embodiment described herein storesthe values A, B, C, and α in a table in the memory 180 separate from thesoftware code to promote flexibility. For example, separate storage ofthe values A, B, C, and α can allow the same software program to be usedin meters that may have different features, and thus different constantsA, B, C, and α.

In any event, after obtaining the values A, B, C, and α in step 310 inthis embodiment, the processing circuit 164 proceeds to step 315. Instep 315, the processing circuit performs the calculation to obtain theraw adjustment value CSH for the current iteration. As discussed above,this value is equal to:CSH=A*I _(SUM) ² +B*I _(SUM) +C,  (1)The value CSH represents the steady-state self-heating adjustment if thecurrent remained at the level I_(SUM) for a long period of time.

Thereafter, in step 320, the processing circuit 164 filters the steadystate self-heating estimate CSH through the IIR filter of equation (2),or CSH′=α*CSH+(1−α)*PREV_CSH′. The resulting value CHS′ represents theestimate of the current measure of self-heating within the meter 112under normal conditions, for example, when there is no arcing in theblades 156 and/or sockets 124, 128, nor any other heat-generatingmalfunction. The self-heating estimate CSH′ is useful because it makesit easier to determine whether a heat-generating malfunction is presentmore accurately, particular when the temperature sensor 160 is locatedaway from the current coils or blades 140, for example, on the printedcircuit board 137, or within the integrated circuit chip 170 itself.

In step 325, the processing circuit 164 stores the current CSH′ value asthe value PREV_CHS′ for use in step 320 in the subsequent iteration ofthe steps 300. The processing circuit 164 in step 330 obtains thecurrent temperature sensor value TM from the temperature sensor 160. Asdiscussed above, the value TM will be influenced by the current ambient(external environmental) temperature ET, the meter self-heating undernormal conditions CSH′, and any heat generating malfunction.

In step 335, the processing circuit 164 adjusts the temperature sensorvalue TM by subtracting out the value CSH′. The resulting temperaturevalue HE represents the measured temperature, with the estimatedself-heating (for normal operations) removed. Thus, under normalconditions, the temperature value HE should be close to the ambienttemperature ET. As such, any significant difference between HE and ETcan indicate a heat-generating malfunction within the meter 112, or inor on the meter blades 156.

In step 340, the processing circuit 164 obtains a threshold TH, which isa function of date and time, that identifies an overheating threshold.The overheating threshold TH is adjusted for time of day and seasonaltemperature trends. Further detail on one useful embodiment forproviding the threshold TH as a function of time and date is providedbelow in connection with FIGS. 4 through 8. In an alternativeembodiment, if the processing circuit 164 can obtain the true localexternal temperature ET from an external (e.g. remote) source oftemperature information, the value TH can be set to that value plus apredetermined buffer of a few degrees, ET+δ. In any event, after theprocessing circuit 164 obtains the threshold TH in step 340, theprocessing circuit 164 proceeds to step 345.

In step 345, the processing circuit 164 determines whether the value HEexceeds TH. If so, then the processing circuit 164 proceeds to step 350.If not, however, then the processing circuit 164 proceeds to step 355,discussed further below.

In step 350, the processing circuit 164 stores in the memory 180 anindication (e.g. an overheat flag) that a heat-generating anomaly orevent has been detected. The indication may be stored within apredetermined position in a predefined data table, such that an externalcomputing device communicating with the meter processing circuit 164 mayreceive the table data and determine the existence of theheat-generating event has been detected. Similarly, the processingcircuit 164 may also cause the communication circuit 184 to transmit asignal indicating the event to an external device, such as a centralcomputer monitored by the utility service provider. The processingcircuit may also, or alternatively, cause the display 188 to display anindication of the event, and/or cause the service switch 172 to open,thereby interrupting the current through the meter 112. It is noted thatit could be advantageous to require multiple detections of aheat-generating anomaly (i.e. in subsequent executions of the routine300) before communicating the indication, displaying the indication,and/or opening the service switch 172.

In the present embodiment, the processing circuit 164 maintains twoseparate overheat flags indicating first and second levels of severity.To this end, FIG. 4 shows in further detail an exemplary set ofoperations that may be used as step 350 of FIG. 3.

Referring to FIG. 4, the processing circuit executes step 405 as aresult of the processing circuit 164 determining in step 345, that theHE>TH. In step 405, the processing circuit 164 determines whetherHE>TH+Δ, where Δ represents the difference between a first level alarm(e.g. an “overheat warning”), and a second level alarm (e.g. an“overheat alarm”). If HE≤TH+Δ, then the processing circuit 164 proceedsto step 410. If, however, HE>TH+Δ, then the processing circuit 164proceeds to step 420.

In step 410, the processing circuit 164 stores two first level alarmflags in the memory 180, e.g. “overheat warning” flags. One first levelalarm flag is persistent, and can only be set once, and only reset by atechnician. The other first level alarm flag is a present conditionindicator, and can be reset at any time the condition is no longerpresent. This present condition indicator flag, for example, can bereset in step 355, discussed further below. Thereafter, in step 415, theprocessing circuit 164 causes a visual indication of the setting of thefirst level alarm flag(s) on the display 188. The processing circuit 164thereafter returns to step 360 of FIG. 3.

By contrast, in step 420, the processing circuit 164 stores two secondlevel alarm flags in the memory 180, e.g. “overheat alarm” flags. Onesecond level alarm flag is persistent, and can only be set once, andonly reset by a technician. The other second level alarm flag is apresent condition indicator flag, similar to the first level presentcondition indicator flag, discussed above in connection with step 410.Thereafter, in step 425, the processing circuit 164 causes a visualindication of the setting of the second level alarm flag(s) on thedisplay 188. The processing circuit 164 may also open the service switch172, or cause communication of the presence of the condition by thetransceiver 184. The processing circuit 164 thereafter returns to step360 of FIG. 3.

As discussed above, the first and second level persistent flags can onlybe cleared by a process that involves interaction with a technician fromthe utility. Thus, the indication of either or both flags also persistsuntil cleared by a utility technician.

Referring again to FIG. 3, step 355 occurs if is determined in step 340that no overheat condition currently exists, or in other words, HE≤TH.The processing circuit in step 355 clears either or both of the presentcondition indicator flags set, if either had been set per steps 410 and420. The processing circuit 164 thereafter proceeds to step 360.

In step 360, the processing circuit 164 completes the routine 300. Aftera predetermined time, the processing circuit 164 returns to step 305re-execute the routine 300 for the next time period interval.

It will be appreciated that the value HE, which approximates theexternal ambient temperature under normal conditions, may be useful forother functions. For example, some meters perform a load-profilingoperation in which energy usage and other values are stored forsuccessive time increments (e.g. every 5 to 30 minute interval) to allowusage patterns and condition patterns to be analyzed. Someload-profiling operations also store ambient temperature, if availablefor each load profiling time interval. Thus, the processing circuit 164in this embodiment may store the value HE, or an average of such avalue, for each load profiling time interval (along with energyconsumption and other information), the load profiling log stored in thememory 180. However, the processing circuit 164 may be configured toavoid storing the HE value if it exceeds the threshold TH, as thatnumber would be influenced by overheating conditions.

It can thus be seen that the processing circuit 164 can use methods toallow a temperature sensor 160, which may be located some distance fromthe source of arcing or other heating anomaly, to detect an abnormalconditions that is timely adjusted for meter self-heating under normalconditions, and to otherwise approximate the external air temperature.

As discussed above, the threshold TH is preferably based on a currentexpected or real ambient temperature, plus a margin of a few degrees.For example, if the current ambient temperature ET(n) is known to be 20°C., then the threshold TH may be 25° C. As discussed above, theprocessing circuit 164 may be configured in some embodiments to receivecurrent, accurate ambient temperature information from external sourcesvia the communication circuit 184. However, if access to the realambient temperature ET(n) is not available, then the threshold TH shouldbe set to a maximum expected ambient temperature.

In a very simple case, a single threshold TH for the maximum temperaturemay be used. Thus, for example, the threshold of 65° C. may be used inmoderate climates, due to sunlight loading. However, using a singlethreshold is disadvantageous because for most of the year, averagetemperatures are far below 65° C., particularly at night. As a result,it will take more potentially damaging internal overheating to cause theHE(n) to exceed TH.

To address this issue, one embodiment of the invention employs athreshold TH that is a function of time and date. In this embodiment,the processing circuit 164 maintains a real-time clock and calendar, asis well-known in the metering art. The processing circuit 164 obtains athreshold TH that is based on a maximum expected temperature for thedate, and for that date, the maximum expected temperature for the timeof day. In this embodiment, the threshold TH is selected from a set ofstored thresholds TH_(M,D), each corresponding to a combination M,D of atime of year M and a time of day D. In this embodiment, the set ofstored thresholds TH_(M,D) include two estimated maximum temperaturethresholds (night and day) for each month of the calendar year. Thus,the memory 180 stores twenty-four values TH_(M,D), with two thresholds,D=0 (night) and D=1 (day) for each month M=1 to 12.

By way of example, at 12:08 pm on February 4th, the processing circuit164 in step 340 would retrieve as the threshold TH the value TH_(2,1)from memory. At 11:30 pm on July 18^(th), the processing circuit 164would retrieve as the threshold TH the value TH_(7,0). In addition, inthe embodiment described herein, the memory 130 further stores anadditional threshold, TH_(0,0), that is used if the time and date is notpresently available (e.g. due to a recent power interruption or meterrestart).

In this embodiment, step 340 of FIG. 3 may be carried out as illustratedby the operations of FIG. 5. Referring to step 5, the processor 164 instep 505 determines whether the real-time clock has a sufficientlyaccurate value. As discussed above, the processor 164 and/or othercircuits are configured to maintain the real-time clock (including date)during normal meter operation and even during most power outages.However, there are conditions in which the processor 164 loses thereal-time clock, such as during very long power outages or othermalfunctions. The processor 164 will store a value or flag indicative ofa failure/loss of the real-time clock. If the processor 164 in step 505determines that the real-time clock has a sufficiently accurate value,then the processor 164 proceeds to step 510. If, however, processor 164in step 505 determines that the real-time clock does not have asufficiently accurate value, then the processor 164 proceeds to step515.

Referring now to step 510, the processor 164 retrieves as M the monthvalue from the real-time clock. Thereafter the processor 164 in step 520determines whether the time of day is in or around daylight hours, forexample, between 6:00 am and 9:00 pm. In this embodiment, the real-timeclock employs a twenty-four hour format. Thus, the processor 164determines in step 520 whether the hour value HR is greater than asunrise time value SR, but less than a sunset time value SS. The valuesSR and SS may be constant, but preferably vary as a function of date, asthe number of daylight hours varies throughout the year. If the valuesSR are based on date, then the memory 180 preferably stores values SRand SS that are also a function of date, for example, the month value M.In such a case the processor 164 retrieves the values SR and SS from thememory 180 to carry out the operations of step 520.

If the processing circuit 164 determines that SR<HR<SS, then theprocessing circuit 164 sets the value D to 1 in step 525. If not, thenprocessing circuit 164 sets the value D to 0 in step 530. After eitherof steps 525 or 530, the processing circuit 164 executes step 535. Instep 535, the processing circuit 164 sets the threshold value TM equalto the array value TM_(M,D). After step 535, the processing circuit 164has completed step 340 of FIG. 3 and can proceed to step 345 asdescribed above.

It will be appreciated, however, that other methods of employing thevalue TM_(M,D) in the operations of FIG. 3 may be used.

Referring again to step 515, which occurs when the real-time clock isnot accurate, the processor 164 sets both M and D to 0. The processingcircuit 164 thereafter proceeds to step 535 to set TM=TM_(0,0). TheTM_(0,0) value is preferably set to (or at least based on) the maximumtemperature threshold in the array TM_(M,D), to reduce the occurrencesof false positives from ambient temperature.

FIG. 6 shows an exemplary timeline of the values of that occur in asample operation of meter 112, which help illustrate the operations ofthe exemplary embodiment of FIGS. 3 and 5 described above. FIG. 6 showsa timeline graph 600 of temperature versus time over a twenty-seven (27)hour period in the month of July. The timeline values include themeasured temperature value TM(n) generated by the temperature sensor 160(line 602), the adjusted temperature HE generated in step 335 (line604). and the true ambient temperature (e.g. environmental temperature)ET, which is not available within the meter 112 (line 606). The timelinevalues also include the first threshold value TH obtained in step 340 ofFIG. 3 (line 608) and the second threshold value TH+Δ used in step 405of FIG. 4 (line 610).

The values of FIG. 6 represent a time in which no heat was generatedwithin the meter 112 due to malfunction or arcing in the current blade156. In other words, the values of FIG. 5 illustrate a normal operationof the meter 112. As illustrated by the lines 602 and 606, thedifference between the true ambient temperature (606) and the measuredtemperature (602) can vary significantly. This variance is due to themeter self-heating factors discussed further above. It is also notedthat the differences are exaggerated in the late afternoon and earlyevening, for example, from about 6:00 pm (18:00) to 10:00 pm (22:00).Such exaggerated differences are likely due to elevated current usage,which tends to occur in the late afternoon or evening in residences,particularly in summer months. The elevated current usage increases themeter self-heating significantly, which is reflected in the value CSH ofequation (1).

It is also noted that the measured temperature 602 has higher frequency(e.g. hourly) variance occurring at intervals, particularly during theday. Such high frequency variations can be due, for example, totemporary increases in current from devices that operate periodically.

As shown in FIG. 6, the compensated temperature HE line 504 does not inthis embodiment exactly track the true ambient temperature line 506.This is due to the fact that some sources of error are difficult topredict. For example, sunlight loading can introduce, depending on theamount of cloud cover, a large degree of difference between the sensedtemperature within the meter 112 and the external ambient temperature.In this embodiment, it has been determined that the increase in accuracyin the compensated temperature HE does not improve performancesufficiently to justify the increase in complexity necessary to achievesuch accuracy. However, other embodiments can vary and account fordifferent or additional factors to improve accuracy, if desired.

Nevertheless, it can be seen that the compensated temperature HE line604 eliminates a large part of the error in the measured temperature TMline 606. Also, the compensated temperature HE line 604 does not reflectthe higher frequency fluctuations in the measured temperature TM line606, which further indicates that the fluctuations are due to periods ofheavy current usage.

Referring to the first threshold value TH, the line 608 toggles betweenthe daytime level TH_(7,1) and the nighttime level TH_(7,0). The secondthreshold value TH+Δ, the line 610 toggles between the daytime levelTH_(7,1)+Δ and the nighttime level TH_(7,0)+Δ. It can be seen that theunadjusted measurement TM would exceed the threshold from the times of21:00 to 22:00 causing a warning and alarm, if it were compared to thethresholds TH and/or TH+Δ, resulting a false event. In the prior art,the only way to avoid such false events would be to increase thethresholds significantly, which would be undesirable because a truearcing condition could take longer to detect.

In this embodiment, the threshold values TH can only have one of twovalues for a given day. However, in an alternative embodiment shown inFIG. 7, the threshold value line 708 has a trapezoidal shape, employingtransition areas 712, 714 where the threshold varies between the valuesTH_(7,1) and the nighttime level TH_(7,0) as a function of time. In thiscase, the threshold value TH varies as a linear function of time in thetransition areas 712, 714. The trapezoidal shape accommodates thetransition areas between night and day to further improve theresponsiveness to a relatively rapidly developing overheat situation.The upper threshold, TH+Δ, has the same shape, as indicated by line 710.This feature, combined with daylight transition time values SR and SScan create a robust overheat detection operation.

FIG. 8 illustrates an alternative set of operations that can be used asstep 340 of FIG. 3 to implement the trapezoidal shape threshold line 708of FIG. 7. Referring to FIG. 8, the processing circuit 164 in step 805determines whether the real-time clock has a sufficiently accuratevalue, as per step 505 of FIG. 5. If the processing circuit 164determines that the real-time clock has a sufficiently accurate value,then the processing circuit 164 proceeds to step 810. If, however, theprocessing circuit 164 determines that the real-time clock does not havea sufficiently accurate value, then the processor 164 proceeds to step815.

Referring now to step 810, the processor 164 retrieves as M the monthvalue from the real-time clock. Thereafter, the processor 164 in step820 determines which of four conditions exist based on the time of day,the sunrise time value SR, and the sunset time value SS. Theseconditions relate generally to daylight hours, nighttime hours, atransition time (TTND) from night to day, and a transition time (TTDN)from day to night. Table 1 shows the possible conditions:

TABLE 1 1. SR + TTND < HR < SS (daylight) 2. (HR > SS + TTDN) or (HR <SR) (nighttime) 3. SR ≤ HR ≤ SR + TTND (transition) 4. SS ≤ HR ≤ SS +TTDN (transition)As noted above in connection with FIG. 5, the values of SR and SS mayvary throughout the calendar year. Thus, step 810 may further includeretrieving from memory 180 the values of SR and SS, based on the dateinformation in the real-time clock. For example, the values SR and SSmay be retrieved based on the month value of M. In addition, thetransition time values TTND and TTDN may be constant, and be the same.In the example of FIG. 7, the value of each of TTND and TTDN is two (2)hours.

The processing circuit 164 then proceeds based on which of theconditions 1 to 4 exists. If condition 1 exists, then the processingcircuit 164 executes step 825. If condition 2 exists, then theprocessing circuit 164 executes step 830. If condition 3 exists, thenthe processing circuit 164 executes step 835. If condition 4 exists,then the processing circuit 164 executes step 840.

In step 825, the processing circuit 164 sets the threshold value TH toTH_(M,1), and then proceeds to step 845. In step 830, the processingcircuit 164 sets the threshold value TH to TH_(M,0), and then proceedsto step 845. In step 835, the processing circuit 164 sets the thresholdvalue TH to:

$\begin{matrix}{{TM} = {{TM}_{M,0} + {\left( \frac{{TM}_{M,1} - {TM}_{M,0}}{TTND} \right)\left( {{CV} - {SR}} \right)}}} & (3)\end{matrix}$where CV is the current clock value. The equation represents the linearslope between 6:00 and 8:00 on FIG. 7. After step 835, the processingcircuit 164 proceeds to step 845. In step 840, the processing circuit164 sets the threshold value TH to:

$\begin{matrix}{{TM} = {{TM}_{M,1} + {\left( \frac{{TM}_{M,0} - {TM}_{M,1}}{TTDN} \right)\left( {{CV} - {SS}} \right)}}} & (4)\end{matrix}$where CV is the current clock value. The equation represents the linearslope between 19:00 and 21:00 on FIG. 7. After step 840, the processingcircuit 164 proceeds to step 845.

In step 845, the processing circuit 164 has completed step 340 of FIG. 3by obtaining the proper value TH, and can proceed to step 345 asdescribed above.

Referring again to step 815, which occurs when the real-time clock isnot accurate, the processing circuit 164 sets TH=TH_(0,0). Theprocessing circuit 164 thereafter proceeds to step 845. The TH_(0,0)value is preferably set to (or at least based on) the maximumtemperature threshold in the array TH_(M,D), to reduce the occurrencesof false positives from ambient temperature.

The operations of FIG. 8 thus provide an improved, but more complexversion of the variable, time dependent thresholds discussed above inconnection with FIGS. 5 and 6. It will be appreciated that the variablethresholds described herein have utility even in meters that do notemploy temperature adjustments. For example, physical location of thetemperature sensor 160 in another part of the meter 112, for example,near the blades 156, may obviate the need for temperature compensation,or may only require minor current-based temperature compensation. Insuch a case, however, the time-dependent thresholds discussed inconnection with FIGS. 5 to 8 would nevertheless provide advantages.

It will also be appreciated that the system may be configured to usemore than twelve sets of daily thresholds (one set per month) as taughtherein. For example, it may be sufficient to include as few as foursets, particularly in warm climates, and it may be advantageous toinclude more than twelve sets in some cases.

Moreover, it will be appreciated that the temperature measurementcompensation operations described further above have utility even incases where a single threshold is used regardless of time or date. Inaddition, it will be appreciate that the combination of temperatureadjustment and threshold comparisons may be carried out in multiple,mathematically equivalent ways. Additionally, it will be appreciatedthat although the meter 112 is described as using current sensors in theform of current transformers, it will be appreciated that the inventionsdescribed herein are readily applicable to meters that employ othertypes of current measurement devices (e.g. shunts) that work with orinclude a conductor (referred to herein as a current coil or primarycoil) carrying large magnitude currents.

In addition, it has been experimentally determined that the effects ofattenuated heat transfer from a meter current coil (i.e. load carryingconductor) to a board mounted sensor are significant at air gaps as lowas 0.1 inches. Thus, the embodiments described above can offeradvantages when the temperature sensor is as little as 0.1 inches awayfrom the current coil. Accordingly, in other configurations in which atleast the same amount of thermal insulation separates the temperaturesensor from the current coil, the inventive techniques described herewould demonstrate advantages.

It will therefore be understood that the above-described embodiments aremerely illustrative, and that those of ordinary skill in the art mayreadily devise their own modifications that incorporate the principlesof various aspects of the present invention and fall within the spiritand scope thereof.

What is claimed is:
 1. A utility meter comprising: a meter housing; atleast one current coil supported on the meter housing and configured tobe operably coupled to a meter socket to receive heat energy from themeter socket; a temperature sensor disposed within the meter housing andconfigured to generate a sensor signal based on a temperature within themeter housing; and a processing circuit within the metering housingoperably coupled to the temperature sensor and configured to: (i) obtainthe sensor signal and generate meter temperature information based atleast in part thereon; (ii) obtain a first predetermined threshold basedon at least one of time of day information and date information; (iii)determine whether an abnormal condition exists by comparing the metertemperature information to a value based on the first predeterminedthreshold; and (iv) generate an output signal to a memory, display orcommunication circuit responsive to determining that the abnormalcondition exists.
 2. The utility meter of claim 1, further comprisingthe communication circuit, and wherein the communication circuit isconfigured to communicate information indicating a maintenance event toa computing device external to the computer.
 3. The utility meter ofclaim 1, wherein the value is or directly represents the firstpredetermined threshold.
 4. The utility meter of claim 3, furthercomprising a memory storing a plurality of thresholds, and wherein theprocessing circuit is further configured to obtain the firstpredetermined threshold at least in part by selecting one of theplurality of thresholds stored in memory based on at least one of timeof day information and date information.
 5. The utility meter of claim4, wherein the processing circuit is further configured to obtain thefirst predetermined threshold at least in part by selecting one of theplurality of thresholds stored in memory based on time of dayinformation and further based on date information.
 6. The utility meterof claim 5, wherein, for a given date, the processing circuit isconfigured to select the one of the plurality of thresholds from twothresholds.
 7. The utility meter of claim 1, wherein the value is afunction of the first predetermined threshold and an additionalpredetermined threshold.
 8. The utility meter of claim 1, wherein theprocessing circuit is further configured to, based on the time of dayinformation: obtain the additional predetermined threshold based on thedate information.
 9. The utility meter of claim 8, wherein theprocessing circuit is configured to generate the value from the firstpredetermined threshold, the second predetermined threshold, and thetime of day information.
 10. The utility meter of claim 9, wherein theprocessing circuit is configured to determine the value as a function oftime, the value being between the first predetermined threshold and thesecond predetermined threshold.
 11. A utility meter comprising: a meterhousing; a display supported within the meter housing; at least onecurrent coil supported on the meter housing and configured to beoperably coupled to a meter socket to receive heat energy from the metersocket; a temperature sensor disposed within the meter housing andconfigured to generate a sensor signal based on a temperature within themeter housing; and a processing circuit within the metering housingoperably coupled to the at least one current coil to obtain voltage andcurrent measurement information related to voltage and current on the atleast one current coil, the processing circuit further operably coupledto the temperature sensor and configured to, (i) generate and causedisplay of energy consumption information based on the obtained voltageand current measurement information; (ii) obtain the sensor signal andgenerate meter temperature information based at least in part thereon;(iii) obtain a first predetermined threshold based on at least one oftime of day information and date information; (iv) determine whether anabnormal condition exists by comparing the meter temperature informationto a value based on the first predetermined threshold; and (v) generatean output signal to a memory, display or communication circuitresponsive to determining that the abnormal condition exists.
 12. Theutility meter of claim 11, wherein the value is or directly representsthe first predetermined threshold.
 13. The utility meter of claim 12,further comprising a memory storing a plurality of thresholds, andwherein the processing circuit is further configured to obtain the firstpredetermined threshold at least in part by selecting one of theplurality of thresholds stored in memory based on at least one of timeof day information and date information.
 14. The utility meter of claim13, wherein the processing circuit is further configured to obtain thefirst predetermined threshold at least in part by selecting one of theplurality of thresholds stored in memory based on time of dayinformation and further based on date information.
 15. The utility meterof claim 14, wherein, for a given date, the processing circuit isconfigured to select the one of the plurality of thresholds from twothresholds.
 16. The utility meter of claim 11, wherein the value is afunction of the first predetermined threshold and an additionalpredetermined threshold.
 17. The utility meter of claim 11, wherein theprocessing circuit is further configured to, based on the time of dayinformation: obtain the additional predetermined threshold based on thedate information.
 18. The utility meter of claim 17, wherein theprocessing circuit is configured to generate the value from the firstpredetermined threshold, the second predetermined threshold, and thetime of day information.